Chemistry Problem Solutions

Q7 The properties of copper that makes it to be used in electrical cables and water pipes is that copper is a very good conductor of both heat and electricity. Copper is also malleable hence can be easy to hammered mould into different thin shapes required in making pipes and electrical cables. It is also resists corrosion from air, sea water and moisture. Copper is also durable.

Q8(i)  metal salts are soluble in water. They are good conductors of electricity in molten state .their free electrons in molten state conduct both thermal heat and electricity.

ii) Metal ions in the metal salts are reactive; they can get oxidized in the process of cooking when they are subjected to heat. Most metal salts are corrosive and can corrode the container used for making saucepans.

iii) Metal salts are used in making jewels and in the galvanization process.  metal salts like calcium salts produce orange-red color, strontium salts produce bright red, and barium salts produces yellow green colors flames. This property of metal salts can be used in coloring fireworks display e.g gold chlorides. They are used in thermometers because of their good thermal conductivity. They are used in corrosion protection and surface finishing, decoration, electro-refining

Q9) The free electrons in covalent bonded compounds are used in bonding. This means that there are no free electrons left to conduct electricity. In ironically bonded compounds, the ions in the compounds may get dissolved in the water thereby making the water contaminated. The ions may also corrode the surface of the metal pipes.

Q10)

The atoms in diamond are held together by strong covalent bonds. This makes it to have high melting point. To break the covalent intra-molecular bonds, high melting temperatures are required. Diamond structure has face-centered cube lattice. Each carbon atom is bonded to four other carbon atoms by strong covalent bonds. On the other hand iodine is a molecular solid. Each iodine molecule contains two atoms that are held together by a strong covalent bond. These molecules are held together by weak molecular forces. This is the reason why it has low melting point.ie the weak molecular forces between the lattices of iodine molecules.

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Q15.Take a substance containing potassium in a test tube and add water.   Add aqueous ammonia. The absence of the precipitate indicated that potassium ion is present

Flame test for Potassium ion

Take a compound containing potassium ion in a test tube. Dip a glass rod in the solution and immediately put it on a flame of a bunsen burner

Lilac flame confirms the presence of potassium ion in the presence of potassium ions in the compound

Q16

 

Procedure

Put the solid containing iodide ions in a test tube. Add distilled water and stir or swirl.add2M aqueous ammonia to the test tube

Observation

 

Q17.add distilled water to the two white powder. Add barium chloride solution to the solution and observe. Add nitric acid. The white precipitate persistence shows that the powder is ammonium carbonate. The absence of precipitate shows that the powder is sodium carbonate

Q18 Take each substance and put it in separate boiling tube. Put the boiling tube on a burning flame. Observe the color of the gas and put both red and blue litmus paper on the open side of the boiling tube and observe what happens. Put a glowing splint on the boiling tube.

The boiling tube that produces a pop sound is the one known as sodium carbonate. The one that produces brown gas is the one that contains sodium nitrate and the one that changes wet blue litmus paper and decolorize it is the one that contains sodium sulphate.

 

Q19) when the compound containing lithium is put on a flame on the bunsen burner, the bright red or crimsom red color shows that the compound contains lithium compound. When the compound containing sodium compound id burnt on a Bunsen burner flame, brilliant yellow flame confirms that the substance contains sodium

Q20

a)      Blue and red litmus paper

Potassium dichromate

Sulphuric acid

Filter paper

Gas jah

b)      Pass the gas suspected to be sulphur dioxide into acidified potassium dichromate

The orange solution of potassium dichromate turns to green solution due to formation                                 chromium sulphate confirming the gas as sulphur dioxide.

Put wet litmus paper on a gas jah containing a gas suspected to be sulphur dioxide. The moist                            blue litmus paper turns red and then decolorizes it.

Put a filter paper in acidified in a solution of acidified potassium dichromate solution from orange to green.

c)If the test is negative, the wet blue litmus paper remains blue and the filter paper will maintain its color.

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